1. Field of the Invention
The present invention relates to an image display apparatus that can execute displaying and erasing operations of images repeatedly by moving display particles in an electric field and such display particles to be used in the image display apparatus.
2. Description of Related Art
Conventionally, an image display apparatus that displays images by moving display particles in a gaseous phase has been known. The image display apparatus has a structure in which display particles in a powder state are sealed between two substrates at least one of which is transparent, and by generating an electric field between the substrates, the display particles are moved and adhered to one of the substrates so that an image is displayed. Upon driving such an image display apparatus, a voltage is applied between the substrates to generate an electric field, and the display particles are moved along the electric field direction so that by selecting the electric field direction on demand, the displaying and erasing operations of images can be executed repeatedly. However, once the display particles have been adhered to the substrate, the display particles become unmovable in the adhered state to the substrate since the display particles have a comparatively high adhesive force, resulting in problems that the driving voltage needs to be increased and that the contrast between an image portion and a non-image portion deteriorates. In order to reduce the driving voltage and improve the contrast, each of the display particles needs to maintain appropriate charge thereon.
As a method for producing display particles for an image display apparatus, a pulverizing method has been known in which, after a resin and a colorant have been mixed and kneaded into pellets, the pellets are pulverized and classified so as to obtain particles having a target particle size. Moreover, it has been known that the pulverizing method makes it possible to fill a comparatively large amount of colorants. However, in the display particles obtained through the pulverizing method, the colorant tends to be exposed to the particle surface to make it difficult to maintain electric charge, resulting in degradation of the contrast between an image portion and a non-image portion from the initial driving stage. In a case where, in order to improve the contrast, the content of the colorant is set to a comparatively high level, the exposure of the colorant onto the particle surface becomes conspicuous to cause further degradation of the contrast. Moreover, since the particles obtained by the pulverizing method have a low degree of roundness to cause high physical adhesive force between the substrate and the particles, a higher driving voltage is required.
In particular, the white colorant is poor in its tinting property, with the result that the white display particles, obtained by using the white colorant, tend to fail to provide a sufficient degree of whiteness. Consequently, in a case where white display particles are formed by the pulverizing method using a comparatively large amount of the white colorant, the exposure of the colorant becomes conspicuous correspondingly, with the result that the initial contrast is lowered and the degradation of the contrast becomes further conspicuous on driving repeatedly.
It is an object of the present invention to provide display particles for an image display apparatus as well as such an image display apparatus that can reduce a driving voltage, and repeatedly display images having sufficiently superior contrast between an image portion and a non-image portion for a long period of time.